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ID Date Author Type Category Subject
  945   Fri Apr 27 10:30:57 2012 FrankNotesAcousticsacoustic damping from plexiglas and sandwich structures

sandwich structures using plexiglas : "Damped Windows for Aircraft Interior Noise Control" http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.79.9176

bare plexiglas: http://www.eplastics.com/Plastic/Plastics_Library/Plexiglass-Noise-Reduction

 

  944   Fri Apr 27 08:57:38 2012 steveNotesPurchasesvibration isolators (table legs) in 40m

Those are the ones we are using right now and break after some while because they are too old (the rolling rubber diaphragm is too brittle now and you get small cracks). The tables were resting on the rubber for 15 years and they've been not used floating for the last decade or more. The leakage is small so that you don't feel or hear it (soap water does not work when installed. Pressure loss is 15psi of a 3gal compressor within 1 hour or so, not big but enough to be annoying. We wouldn't care if we would have a constant high pressure air supply.

Quote:

Quote:

The price for the custom made legs are $ 9295, and for the standard 16" are $ 3710

Quote:

We have "Pneumatic Vibration Isolators with Automatic Re-leveling". Height is 16in from top to bottom, so that would raise the table height by 2.5in which i think is not gonna be a problem as i'm pretty sure we can adjust the height of the horizontal beams of the frame and don't have other constraints except the clearance of the ion pump to the HEPA which should be fine. Do you have a price for the 16" ones? (S-2000A-416). The problem with the new legs could be how to mount the table to them. The mounting looks different (diameter, holes etc.)

We should probably consider using the newer version we have currently under the cryo table and the table in the richter lab. Using those would eliminate the need of working on our frame and those tables don't really care what legs they are using at the moment.

 

 

 

 We have 4 Newport XL-A  legs 13.5" high in the 40m. You can try them. You may have to replace some of the floating actuators but otherwise they should work just fine. 

 

  943   Fri Apr 27 08:46:24 2012 FrankNotesopticwindows for vacuum chamber

cavity mirrors are parallel to the end surface of the chamber (not completely, but pretty close; changes every time we touch the stack as we can't fully control the position after sliding the stack into the long chamber. However we should rethink our procedure how we align the stack once in the chamber)

Quote:

Quote:

I don't know how you gonna make the knife edge on the 10" flange of centered and wedged! If you put the small CF flanges on the big one you have parasitic cavities between the window and the cavity even if the window is wedged (only the outside is tilted relative to the flange, the inside is parallel by design. I also suggest going for a metal seal, but not copper as getting those knife edges will be complicated and expensive i guess. So why not using indium or the other single-use metal seal replacement techniques for o-rings available and you only need a flat surface on the big flange and a few tapped blind holes?

Quote:

I asked Steve about the choices, he thought the Thorlabs window should be ok for us.

      What Steve suggested are:

  • The seal between the 10" blank and the windows should be copper seal, (the window already comes with knife edge),so
  • the blank will have knife edge seals for two small windows as well.
  • Thorlabs window does not have an o-ring between the window frame and the optic, we should add the o-ring between them to avoid a direct metal-glass contact.

About the blank with two openings for beam access, he said a vacuum company could do it for us. I'll make a drawing and get a quote from Nor-Cal and MDC. I have to specify that the blank will be for ultra high vacuum system (UHV).

Quote:

For small window option, I can either have it made from scratch ( based on LIGO's drawing) or buy the commercial windows from Thorlabs. Here I listed down all pros and cons for each choice as I discussed it with Frank. I 'll ask Steve tomorrow for his opinions.

 == Using Thorlabs 2.75" OD windows:==

       Pros

  • easy to replace for damaged optics,
  • ready in short time (parts are in stock)
  • minimum time on machine shop
  • The thickness of the window is only 0.63", It should be able to fit in the set up which has ~ 1" clearance.

      cons:

  • Have more rubber seals in the system due to the design, I'll check Cryo:194 to see what will be the minimum pressure we need.

==Making custom parts (like LIGO, see quote window)==

     Pros:

  • There are only one o-ring used for each window (better vacuum pressure)

     cons:

  • Spend more time on designing/machining, probably more money for making the parts as well.
  • Take longer time if we need more spare pieces.
  • The available space for the window is quite limited (1"). If we follow what Zach did for Gyro, it is already to thick for our setup

Quote:

 

I'm searching DCC for window/viewport examples. The following drawings give me some ideas how to make a window for our setup.

 TCS viewports details

double viewports

septum window flange

 

 

 

 Request 2 degrees off set the the 2.75"cf knife edge and tapped holes on the 10" flange.  The location is custom anyhow. You can gain some space this way.  Or can you tip your chamber? 

Check how parallel you cavity is with your chamber

 

  942   Thu Apr 26 16:57:33 2012 steveNotesPurchasesvibration isolators (table legs) in 40m

Quote:

The price for the custom made legs are $ 9295, and for the standard 16" are $ 3710

Quote:

We have "Pneumatic Vibration Isolators with Automatic Re-leveling". Height is 16in from top to bottom, so that would raise the table height by 2.5in which i think is not gonna be a problem as i'm pretty sure we can adjust the height of the horizontal beams of the frame and don't have other constraints except the clearance of the ion pump to the HEPA which should be fine. Do you have a price for the 16" ones? (S-2000A-416). The problem with the new legs could be how to mount the table to them. The mounting looks different (diameter, holes etc.)

We should probably consider using the newer version we have currently under the cryo table and the table in the richter lab. Using those would eliminate the need of working on our frame and those tables don't really care what legs they are using at the moment.

 

 

 

 We have 4 Newport XL-A  legs 13.5" high in the 40m. You can try them. You may have to replace some of the floating actuators but otherwise they should work just fine. 

  941   Thu Apr 26 12:15:13 2012 FrankNotesPurchasesvibration isolators (table legs)

The price for the custom made legs are $ 9295, and for the standard 16" are $ 3710

Quote:

We have "Pneumatic Vibration Isolators with Automatic Re-leveling". Height is 16in from top to bottom, so that would raise the table height by 2.5in which i think is not gonna be a problem as i'm pretty sure we can adjust the height of the horizontal beams of the frame and don't have other constraints except the clearance of the ion pump to the HEPA which should be fine. Do you have a price for the 16" ones? (S-2000A-416). The problem with the new legs could be how to mount the table to them. The mounting looks different (diameter, holes etc.)

We should probably consider using the newer version we have currently under the cryo table and the table in the richter lab. Using those would eliminate the need of working on our frame and those tables don't really care what legs they are using at the moment.

 

 

 

  940   Thu Apr 26 08:35:57 2012 steveNotesopticwindows for vacuum chamber

Quote:

I don't know how you gonna make the knife edge on the 10" flange of centered and wedged! If you put the small CF flanges on the big one you have parasitic cavities between the window and the cavity even if the window is wedged (only the outside is tilted relative to the flange, the inside is parallel by design. I also suggest going for a metal seal, but not copper as getting those knife edges will be complicated and expensive i guess. So why not using indium or the other single-use metal seal replacement techniques for o-rings available and you only need a flat surface on the big flange and a few tapped blind holes?

Quote:

I asked Steve about the choices, he thought the Thorlabs window should be ok for us.

      What Steve suggested are:

  • The seal between the 10" blank and the windows should be copper seal, (the window already comes with knife edge),so
  • the blank will have knife edge seals for two small windows as well.
  • Thorlabs window does not have an o-ring between the window frame and the optic, we should add the o-ring between them to avoid a direct metal-glass contact.

About the blank with two openings for beam access, he said a vacuum company could do it for us. I'll make a drawing and get a quote from Nor-Cal and MDC. I have to specify that the blank will be for ultra high vacuum system (UHV).

Quote:

For small window option, I can either have it made from scratch ( based on LIGO's drawing) or buy the commercial windows from Thorlabs. Here I listed down all pros and cons for each choice as I discussed it with Frank. I 'll ask Steve tomorrow for his opinions.

 == Using Thorlabs 2.75" OD windows:==

       Pros

  • easy to replace for damaged optics,
  • ready in short time (parts are in stock)
  • minimum time on machine shop
  • The thickness of the window is only 0.63", It should be able to fit in the set up which has ~ 1" clearance.

      cons:

  • Have more rubber seals in the system due to the design, I'll check Cryo:194 to see what will be the minimum pressure we need.

==Making custom parts (like LIGO, see quote window)==

     Pros:

  • There are only one o-ring used for each window (better vacuum pressure)

     cons:

  • Spend more time on designing/machining, probably more money for making the parts as well.
  • Take longer time if we need more spare pieces.
  • The available space for the window is quite limited (1"). If we follow what Zach did for Gyro, it is already to thick for our setup

Quote:

 

I'm searching DCC for window/viewport examples. The following drawings give me some ideas how to make a window for our setup.

 TCS viewports details

double viewports

septum window flange

 

 

 

 Request 2 degrees off set the the 2.75"cf knife edge and tapped holes on the 10" flange.  The location is custom anyhow. You can gain some space this way.  Or can you tip your chamber? 

Check how parallel you cavity is with your chamber

  939   Wed Apr 25 15:15:03 2012 taraNotesLaserborrow NPRO from TNI

Duly noted, I'll write the sop for this one and put it on svn and wiki.

Quote:

Don't forget to write an SOP for that laser before using it. A few things changed recently if you want to use the old SOP as an template. The hazard zone and emergency laser shutdown procedures, table layout etc. have slightly changed since the 10W laser has been moved. The map outside the lab is also not up-to-date anymore. The main kill switch at the door is still active but the second one which was attached to the 10W laser is gone now, but also not required for the NPRO. The required OD for safety glasses has to be recalculated for the document, but the ones we have are all good. The rest of the old SOP should be the same.

You also have to redo the mode matching to the PMC as the beam waist changes if you switch to the higher power laser.

For a two-laser setup we don't have all the parts at the moment to do so. There is no EOM for the PMC nor the refcav sidebands, no servo for the PMC, and no PMC. We don't have all parts to build a new PMC, especially no PZTs. Mirrors exist, spacer parts too but have to be assembled and we have to ask P.K. if we can have them, but shouldn't be a problem.

 

 

 

  938   Wed Apr 25 10:44:29 2012 FrankNotesopticwindows for vacuum chamber

I don't know how you gonna make the knife edge on the 10" flange of centered and wedged! If you put the small CF flanges on the big one you have parasitic cavities between the window and the cavity even if the window is wedged (only the outside is tilted relative to the flange, the inside is parallel by design. I also suggest going for a metal seal, but not copper as getting those knife edges will be complicated and expensive i guess. So why not using indium or the other single-use metal seal replacement techniques for o-rings available and you only need a flat surface on the big flange and a few tapped blind holes?

Quote:

I asked Steve about the choices, he thought the Thorlabs window should be ok for us.

      What Steve suggested are:

  • The seal between the 10" blank and the windows should be copper seal, (the window already comes with knife edge),so
  • the blank will have knife edge seals for two small windows as well.
  • Thorlabs window does not have an o-ring between the window frame and the optic, we should add the o-ring between them to avoid a direct metal-glass contact.

About the blank with two openings for beam access, he said a vacuum company could do it for us. I'll make a drawing and get a quote from Nor-Cal and MDC. I have to specify that the blank will be for ultra high vacuum system (UHV).

Quote:

For small window option, I can either have it made from scratch ( based on LIGO's drawing) or buy the commercial windows from Thorlabs. Here I listed down all pros and cons for each choice as I discussed it with Frank. I 'll ask Steve tomorrow for his opinions.

 == Using Thorlabs 2.75" OD windows:==

       Pros

  • easy to replace for damaged optics,
  • ready in short time (parts are in stock)
  • minimum time on machine shop
  • The thickness of the window is only 0.63", It should be able to fit in the set up which has ~ 1" clearance.

      cons:

  • Have more rubber seals in the system due to the design, I'll check Cryo:194 to see what will be the minimum pressure we need.

==Making custom parts (like LIGO, see quote window)==

     Pros:

  • There are only one o-ring used for each window (better vacuum pressure)

     cons:

  • Spend more time on designing/machining, probably more money for making the parts as well.
  • Take longer time if we need more spare pieces.
  • The available space for the window is quite limited (1"). If we follow what Zach did for Gyro, it is already to thick for our setup

Quote:

 

I'm searching DCC for window/viewport examples. The following drawings give me some ideas how to make a window for our setup.

 TCS viewports details

double viewports

septum window flange

 

 

 

  937   Wed Apr 25 10:23:34 2012 FrankNotesPurchasesvibration isolators (table legs)

We have "Pneumatic Vibration Isolators with Automatic Re-leveling". Height is 16in from top to bottom, so that would raise the table height by 2.5in which i think is not gonna be a problem as i'm pretty sure we can adjust the height of the horizontal beams of the frame and don't have other constraints except the clearance of the ion pump to the HEPA which should be fine. Do you have a price for the 16" ones? (S-2000A-416). The problem with the new legs could be how to mount the table to them. The mounting looks different (diameter, holes etc.)

We should probably consider using the newer version we have currently under the cryo table and the table in the richter lab. Using those would eliminate the need of working on our frame and those tables don't really care what legs they are using at the moment.

Quote:

I'm looking for the new table legs. The height will be 13.5". The plate that connects to the table will have 3 holes, 4" inches away from the center. I need to check what is the weight of the table and if the new legs can be mounted with the table  or not. 

For New port legs, (set of 4), the price are around $2500 (can be cheaper for less weight requirement). I'll check what is the weight of our table.

      They also offer Pneumatic Vibration Isolators with Automatic Re-leveling legs (I don't know what are the differences), but the height are wrong for our setup, the shortest one starts at 16" height. I looked into this category because our current legs also say Pneumatic

 

  936   Wed Apr 25 10:13:55 2012 FrankNotesLaserborrow NPRO from TNI

Don't forget to write an SOP for that laser before using it. A few things changed recently if you want to use the old SOP as an template. The hazard zone and emergency laser shutdown procedures, table layout etc. have slightly changed since the 10W laser has been moved. The map outside the lab is also not up-to-date anymore. The main kill switch at the door is still active but the second one which was attached to the 10W laser is gone now, but also not required for the NPRO. The required OD for safety glasses has to be recalculated for the document, but the ones we have are all good. The rest of the old SOP should be the same.

You also have to redo the mode matching to the PMC as the beam waist changes if you switch to the higher power laser.

For a two-laser setup we don't have all the parts at the moment to do so. There is no EOM for the PMC nor the refcav sidebands, no servo for the PMC, and no PMC. We don't have all parts to build a new PMC, especially no PZTs. Mirrors exist, spacer parts too but have to be assembled and we have to ask P.K. if we can have them, but shouldn't be a problem.

Quote:

I borrow an NPRO from TNI. The model is similar to what we have, but I think the maximum power is 500mW (what we have is 100mW). I'll check the beam waist position tomorrow.

     Since we might switch to 2-laser setup, it is a good idea to have the second one ready. I checked a few companies for 1064 laser diode, but I could not find the information about how to control the frequency and its performance on the webpages. So I asked Eric Black and got the laser from TNI. Plus, the TTFSS is proved to be sufficient to suppress NPRO free running noise below coating noise level, the NPRO laser should be good for our setup.  We might need to think about preparing the rest of the equipments (resonant EOM for 2nd PMC, resonant and Broadband for refcav, PMC, and the servo circuits). For now, if the borrowed laser works fine and has more power, we might just switch it with the current one to gain more power.

 

IMG_0818.jpg

 

  935   Tue Apr 24 22:10:45 2012 taraNotesElectronics Equipmentmodified UPDH

[Frank, Tara]

We checked the input referred noise of the UPDH and found it to be 31nV/rtHz, so we bypassing U6, and the input noise is reduced to 3.3nV/rtHz. Most of the excess noise was introduced at the adjustable gain, U6.

        Before the modification, the noise level at TP13 was 170 nV/rtHz. The gain at U1 was 26.4dB, and -6dB at U6 (0 on the knob). Thus the total amplification was 14.8 (a factor of 5.5). The input referred noise was then 170/5.5 ~ 31 nV/rtHz.   After we scraped out the trace from U6 Vout to TP13, and short TP3 and TP13, the noise at TP13 level was 37nV/rtHz. This level is reasonable (cf OP27 datasheet). The amplification was changed to 20.8 dB (a factor of 11). The input referred noise now is then 37/11 ~ 3.3 nV/rtHz. This input referred noise can be convert to frequency noise by the frequency discriminator gain (latest value was 31kHz/V). It is only 0.1 mHz/rtHz which is  low and will not be the limiting source. This input referred noise will be added to the noise budget. The cavities can be locked properly after the modification. 

 

zoom.png

fig1: part of the schematic of UPDH after modification on R14 and R12, and U6 is bypassed. The whole updated schematic can be found on svn

 

Right now the gain is not adjustable, we will solve this problem later.

  934   Tue Apr 24 22:07:10 2012 taraNotesLaserborrow NPRO from TNI

I borrow an NPRO from TNI. The model is similar to what we have, but I think the maximum power is 500mW (what we have is 100mW). I'll check the beam waist position tomorrow.

     Since we might switch to 2-laser setup, it is a good idea to have the second one ready. I checked a few companies for 1064 laser diode, but I could not find the information about how to control the frequency and its performance on the webpages. So I asked Eric Black and got the laser from TNI. Plus, the TTFSS is proved to be sufficient to suppress NPRO free running noise below coating noise level, the NPRO laser should be good for our setup.  We might need to think about preparing the rest of the equipments (resonant EOM for 2nd PMC, resonant and Broadband for refcav, PMC, and the servo circuits). For now, if the borrowed laser works fine and has more power, we might just switch it with the current one to gain more power.

 

IMG_0818.jpg

  933   Mon Apr 23 22:06:14 2012 taraNotesPurchasesvibration isolators (table legs)

I'm looking for the new table legs. The height will be 13.5". The plate that connects to the table will have 3 holes, 4" inches away from the center. I need to check what is the weight of the table and if the new legs can be mounted with the table  or not. 

For New port legs, (set of 4), the price are around $2500 (can be cheaper for less weight requirement). I'll check what is the weight of our table.

      They also offer Pneumatic Vibration Isolators with Automatic Re-leveling legs (I don't know what are the differences), but the height are wrong for our setup, the shortest one starts at 16" height. I looked into this category because our current legs also say Pneumatic

IMG_0809.jpg 

 

IMG_0805.jpg

  932   Mon Apr 23 16:52:16 2012 taraNotesopticwindows for vacuum chamber

I asked Steve about the choices, he thought the Thorlabs window should be ok for us.

      What Steve suggested are:

  • The seal between the 10" blank and the windows should be copper seal, (the window already comes with knife edge),so
  • the blank will have knife edge seals for two small windows as well.
  • Thorlabs window does not have an o-ring between the window frame and the optic, we should add the o-ring between them to avoid a direct metal-glass contact.

About the blank with two openings for beam access, he said a vacuum company could do it for us. I'll make a drawing and get a quote from Nor-Cal and MDC. I have to specify that the blank will be for ultra high vacuum system (UHV).

Quote:

For small window option, I can either have it made from scratch ( based on LIGO's drawing) or buy the commercial windows from Thorlabs. Here I listed down all pros and cons for each choice as I discussed it with Frank. I 'll ask Steve tomorrow for his opinions.

 == Using Thorlabs 2.75" OD windows:==

       Pros

  • easy to replace for damaged optics,
  • ready in short time (parts are in stock)
  • minimum time on machine shop
  • The thickness of the window is only 0.63", It should be able to fit in the set up which has ~ 1" clearance.

      cons:

  • Have more rubber seals in the system due to the design, I'll check Cryo:194 to see what will be the minimum pressure we need.

==Making custom parts (like LIGO, see quote window)==

     Pros:

  • There are only one o-ring used for each window (better vacuum pressure)

     cons:

  • Spend more time on designing/machining, probably more money for making the parts as well.
  • Take longer time if we need more spare pieces.
  • The available space for the window is quite limited (1"). If we follow what Zach did for Gyro, it is already to thick for our setup

Quote:

 

I'm searching DCC for window/viewport examples. The following drawings give me some ideas how to make a window for our setup.

 TCS viewports details

double viewports

septum window flange

 

 

  931   Sun Apr 22 23:09:38 2012 taraNotesopticwindows for vacuum chamber

For small window option, I can either have it made from scratch ( based on LIGO's drawing) or buy the commercial windows from Thorlabs. Here I listed down all pros and cons for each choice as I discussed it with Frank. I 'll ask Steve tomorrow for his opinions.

 == Using Thorlabs 2.75" OD windows:==

       Pros

  • easy to replace for damaged optics,
  • ready in short time (parts are in stock)
  • minimum time on machine shop
  • The thickness of the window is only 0.63", It should be able to fit in the set up which has ~ 1" clearance.

      cons:

  • Have more rubber seals in the system due to the design, I'll check Cryo:194 to see what will be the minimum pressure we need.

==Making custom parts (like LIGO, see quote window)==

     Pros:

  • There are only one o-ring used for each window (better vacuum pressure)

     cons:

  • Spend more time on designing/machining, probably more money for making the parts as well.
  • Take longer time if we need more spare pieces.
  • The available space for the window is quite limited (1"). If we follow what Zach did for Gyro, it is already to thick for our setup

Quote:

 

I'm searching DCC for window/viewport examples. The following drawings give me some ideas how to make a window for our setup.

 TCS viewports details

double viewports

septum window flange

 

  930   Sun Apr 22 22:10:17 2012 taraNotesDocumentationProposal is on SVN

The problem is fixed, I just deleted my local folder, check outed from the svn. Now when I commit the subversion, it shows up in docs/CTN_docs/proposal folder. I added Frank's drawing of the spacer in v-3. I'll add more materials later.

Quote:

The proposal for CTN lab is on SVN. The original folder was /CTNlab/docs/Proposal.

 

There is a little problem. I copied all the files from our original folder, and saved them in the /trunk/docs/CTN_docs. After I edited the proposal_v3, and commited, the new file showed up in the original folder. I think the copied files still carry their "svn address" with them, so when I commit them, they show up in the old folder. I'll fix this later.

 

 

  929   Sat Apr 21 00:55:00 2012 frank, taraDailyProgressBEATBeat measurement update

We measured the beat after a few changes in the setup (modulation index, air spring, small enclosure around the beat). We update the noise budget with suppressed laser frequency noise and Marconi's frequency noise in ACAV loop as well. There is not much improvement in the overall beat noise.

A few changes in the setup:

  •  Air Springs: We activated the air springs (it was off because we though it causes the vacuum chamber to move too much during the work), so there is one more seismic isolation stage. The peak at 58 Hz disappears.  However, there are peaks around 6-12 Hz showing up this time. They are probably from the table and the legs that are not set to float the table properly*.
  • Modulation index: now the modulation index is 0.18. I measured the power in the carrier and sideband to calculate the mod index, see PSL:855 . This is the maximum we can have with the 13dBm from Marconi with 4-way splitter (-6dBm),-0.5 dBm loss from the cable, so the power to EOM is 6.5dBm.  With the new mod index, the frequency discriminator gain (inverse) for RCAV/ACAV become 22 and 31 kHz/V.
  • A prototype enclosure box around beat setup: PSL:925.

beat_2012_04_20.png

Updated Traces:

  •   Suppressed Laser frequency noise: Since we changed the OLG of TTFSS by changing the modulation index, we remeasured the OLG of TTFSS, applied to the laser frequency noise (estimated to be 1e4/f Hz/rtHz). Good news, we have enough gain in RCAV loop to suppress the laser noise to coating level. The gain setup for common/fast is 750/750
  •  Frequency noise of Marconi for ACAV: We had not done this so far, so we wanted to make sure that it would not be the limiting source. This is done by dividing the frequency noise of marconi by ACAV OLG TF. We assume that the frequency noise is the same as we measured from the marconi for PLL plotted in the noise budget.
  • Shot noise is updated with the current modulation index (0.18) and cavities visibilities (~80%). It is not shown in the nb because I included it in the PDH detection noise.

* The table legs have small leaks, so we have air compressor to keep the pressure high, PSL:880. It works once every hour when the pressure is low.  The change of pressure can screw up the beam alignment a lot (for example, DC readout from RCAV RFPD can be varied from 100mV - 1.2V, with 1.7V maximum value (off resonance). I think it affects the alignment to AOM and change the diffraction efficiency/ beam shape as well.  It also changes the seismic isolation property. The peaks around 10 Hz show up when the pressure is low.  I'll find new legs from New Port and ask for the quote.

 

==Plan for the next few days==

1) Try using DAQ to measure beat signal, see if we can get rid off the frequency noise from PLL

2) Find out about the new legs(prices/availability)

3) Make the acoustic enclosure box around the whole setup

4) Work on the design for new vacuum windows.

 

  928   Thu Apr 19 21:10:59 2012 FrankNotesDrawingsshort cavities

detailed CAD drawings for the short cavities, mirrors, cavity mount, radiation shields, adapter plates and modified top stack  can be found in the drawings folder on the SVN. Need latest version (2011/2012) of Solidworks to open files.
Also included detailed drawing with all tolerances for the spacer which i used to ask for quotes as a pdf.

  927   Thu Apr 19 19:58:19 2012 taraNotesDocumentationProposal is on SVN

The proposal for CTN lab is on SVN. The original folder was /CTNlab/docs/Proposal.

 

There is a little problem. I copied all the files from our original folder, and saved them in the /trunk/docs/CTN_docs. After I edited the proposal_v3, and commited, the new file showed up in the original folder. I think the copied files still carry their "svn address" with them, so when I commit them, they show up in the old folder. I'll fix this later.

 

  926   Thu Apr 19 03:12:23 2012 taraNotesopticwindows for vacuum chamber

 

I'm searching DCC for window/viewport examples. The following drawings give me some ideas how to make a window for our setup.

 TCS viewports details

double viewports

septum window flange

  925   Wed Apr 18 23:53:01 2012 Frank, TaraDailyProgressFoamsimple insulating box

to test how much insulation we need to reduce our acoustic noise (or air currents) problem we've added a simple aluminum-foil plated styrofoam box around the beat breadboard.
There are plenty of holes for all the beams and cables :

  • two for incoming beams
  • two for the power stabilization
  • aux beam from combining beam splitter
  • reflected beam from beat PD
  • video, power, PD cables,...

Even with all those holes we can already see a reduction with a simple lid on top of it. Due to power outage yesterday we still have no stable system yet, so waiting until tomorrow for measurements.

 IMG098.jpg

  924   Wed Apr 18 02:38:59 2012 taraNotesEOMChange modulation depth for 14.75MHz EOM

I changed the attenuator to -1dBm. From a quick measurement, there's no improvement in the beat signal at high frequency. Any improvement in the band we might be able to see is dominated by acoustic and PLL. [more details later]

Quote:

I increased the power to the 14.75MHz EOM from 0.5 dBm to 3.5 dBm. This was done by changing the attenuator from -6dBm to -3dBm.

As a quick test to see improvement in electronic noise level, I increased the detection gain. The modulation depth was changed from 0.14 to 0.2 rad (following the EOM's paramters in psl:855). I could not see any improvement yet. So I'll try to damp the mechanical peaks in the signal so that flat noise level can be measured better.

 

The slope of error signal for RCAV and ACAV are 44.25/57.62 kHz/V

 

  923   Wed Apr 18 00:49:07 2012 taraDailyProgressopticvibration damping on optics

I planned to measure the beat at night with the air springs activated, but the power went out around 11:45 pm. I think the temperature servo got a kick and it is drifting very fast. So I cannot keep the cavities locked long enough for the low frequency measurement. I'm just turning the systems back on for now.

The laser, 3 Marconis for 14.75MHz EOM, for ACAV AOM, for beat are set back to the original setup, PMC medm screen are back on, the air springs are up and working.

The linux machine is on but I forgot the password, will ask Frank tomorrow.

  922   Tue Apr 17 19:51:54 2012 taraNotesopticwindows for vacuum chamber

If we go with plan2,

1)window and flange

  • I think the window size of 2.75" diameter is the largest size for us ( with 3" clearance between the 2 beams). Thorlabs has a 2.75" window with 1.5" optic,with 1.18" opening, so it might not be compatible with its wedged window:http://www.thorlabs.us/NewGroupPage9.cfm?ObjectGroup_ID=5546 which is only 1" diamter.
  • Or we can order 2.75" flange with 1" bored, from N-C. to use with Thorlabs' window. Though I'm not sure how to assemble the two together.

2) Two Half-Nipple will be welded to the blank on the 10" flange. They will be 3" apart, as the input beams are. We might need something smaller than 2.75" diameter for accessing all the screws.

3)  blank 10" flange: I think Frank said that we have one in the lab. For another one, we can order it from N-C, blank. It is ~$ 300.

 

I'm not sure how to mount the window and the flange together. If we buy the window set from Thorlab, I think it can be directly assemble them similarly to the current 10" flange, see figure below. Or we might need to mount the windows like Zach does for Gyro, see ATF:1601.

 IMG_0757.jpg

 

Quote:

I'm checking the properties/prices/availability of window for the vacuum chamber.

 

Plan1: 10" diameter window (6" window opening)

  •  A&N: ($775), no info on optical quality. This is probably just a regular viewport similar to the one we use.
  • Pfeiffer also offers viewports for visually monitoring, so I think they are not good enough.
  •  MDC fused silica window, for 10" flange ($ 3,297), no optics properties. Only lens grade for ultraviolet are specified, but they claim that for IF also available (viewport)
  • Nor-Cal also has flange for 10" and 2.75" with glass,fused quartz, fused silica material. no optics properties shown.

 Plan2: 10" diameter blank with 2 smaller windows (1.5"/2" diameter)

  •  Thorlabs: 2.75" OD window, 1.18" window (windows are replacable, I think we can switch to CVI windows ) ($244 x2) + machining .
  •   MDC offer 2.73" with 1.5" window, no info on optics properties 

 

 Most of the manufacturers do not have good window for laser with 10" flanges. Finding two smaller windows with good optics properties is probably easier.

 

  921   Mon Apr 16 22:02:08 2012 taraDailyProgressopticvibration damping on optics

I forgot to change the code to disable the air springs, now the seismic coupling makes more sense.

beat_2012_04_15_fixed.png

Quote:

I measured beat signal, after damping most of the optics, realigning the beams to the cavities, measured the slope of error signals and applied it to the measured detection noise.  Acoustics peaks around 200Hz to 1kHz still present.

beat_2012_04_15.png

Fig1: beat measurement, I added shot noise and electronic noise from both cavities to a single trace called detection noise (from measurement).

 I turned off the HEPA fans on the table and on the clean bench before measured the beat signal (after I finished, I turned on the fans as usual).

     The peak at 58 Hz shows up this time. I think this is the peak from beam line motion of the stacks, see PSL:716.  (I think that was before we switched to the softer springs, I'll double check). Note that the air springs were not activated during the measurement, we can try using it and see if there is any improvement.

     There is a good improvement on minimizing the acoustic peaks, although still not enough. Also, increasing the modulation depth seems to help with the flat noise part at high frequency, we may really sit on detection noise.

 

  920   Mon Apr 16 18:17:05 2012 Frank, TaraSummaryNoiseBudgetmechanical resonances

I was told at JILA that anything less than 3/4" thick is lame.

This place has thick stuff:

http://www.estreetplastics.com/Clear_Acrylic_Plexiglass_Sheets_3_4_Thick_s/35.htm

Don't worry about the cost of the plastic - if it helps the noise, we have the money.

  919   Mon Apr 16 16:21:01 2012 taraNotesopticwindows for vacuum chamber

I'm checking the properties/prices/availability of window for the vacuum chamber.

 

Plan1: 10" diameter window (6" window opening)

  •  A&N: ($775), no info on optical quality. This is probably just a regular viewport similar to the one we use.
  • Pfeiffer also offers viewports for visually monitoring, so I think they are not good enough.
  •  MDC fused silica window, for 10" flange ($ 3,297), no optics properties. Only lens grade for ultraviolet are specified, but they claim that for IF also available (viewport)
  • Nor-Cal also has flange for 10" and 2.75" with glass,fused quartz, fused silica material. no optics properties shown.

 Plan2: 10" diameter blank with 2 smaller windows (1.5"/2" diameter)

  •  Thorlabs: 2.75" OD window, 1.18" window (windows are replacable, I think we can switch to CVI windows ) ($244 x2) + machining .
  •   MDC offer 2.73" with 1.5" window, no info on optics properties 

 

 Most of the manufacturers do not have good window for laser with 10" flanges. Finding two smaller windows with good optics properties is probably easier.

  918   Mon Apr 16 15:35:15 2012 Frank, TaraSummaryNoiseBudgetmechanical resonances

we mapped the mechanical resonances in our system using two techniques :

  1. tapping each optical component and check spectrum for excited modes. This technique is difficult as we usually excite a lot of other mechanical modes nearby as well.
  2. exciting everything with white noise (loudspeaker) and then add damping on individual components and checking spectrum which modes we reduce. Very precise but you have to start with the dominant wants and damp them first to see the smaller ones nearby.

resonance frequency is attached to each component. Green background behind numbers means we could verify the frequency using both techniques. Yellow means measured using tapping but could not see using the damping technique as the contribution to the beat signal is to weak. Input optics needs to be checked and finalized. Picture is temporary only.

beatboard_resonances.jpg PDH.jpg

  917   Mon Apr 16 03:42:39 2012 FrankNotesPurchasesacoustic insulation

ordered thin (1in) t-channel aluminum frame parts from mcmaster (similar to bosch framing, but cheaper, link) and other stuff to build a nice acoustic enclosure with access from all sides. Bought the 1/4" plexiglas parts for the lid from drillspot (much cheaper and free shipping). For the side panels i'm thinking about using thin aluminum panels mounted to the outside of the frame (not in the slot) and then using the full depth of 1in of the frame structure for acoustic damping using a combination of  sound absorber-barriers, rubber foam, lead, mass loaded vinyl/Nitrile closed cell foam or anything else. However, putting it in the slot would be easier. Didn't buy foam and stuff. Will wait for the frame being on the table to see what to do.

  916   Mon Apr 16 02:20:58 2012 taraDailyProgressopticvibration damping on optics

I measured beat signal, after damping most of the optics, realigning the beams to the cavities, measured the slope of error signals and applied it to the measured detection noise.  Acoustics peaks around 200Hz to 1kHz still present.

beat_2012_04_15.png

Fig1: beat measurement, I added shot noise and electronic noise from both cavities to a single trace called detection noise (from measurement).

 I turned off the HEPA fans on the table and on the clean bench before measured the beat signal (after I finished, I turned on the fans as usual).

     The peak at 58 Hz shows up this time. I think this is the peak from beam line motion of the stacks, see PSL:716.  (I think that was before we switched to the softer springs, I'll double check). Note that the air springs were not activated during the measurement, we can try using it and see if there is any improvement.

     There is a good improvement on minimizing the acoustic peaks, although still not enough. Also, increasing the modulation depth seems to help with the flat noise part at high frequency, we may really sit on detection noise.

  915   Sat Apr 14 06:03:23 2012 frank,taraDailyProgressopticvibration damping on optics

 We are damping most of the optics with rubber cones. There are a few peaks that we still could not find their origins.  We are thinking to build an acoustic insulation box to cover the setup.

   [details will be added soon]

IMG_0744.jpgIMG_0742.jpg

  914   Sat Apr 14 01:10:48 2012 taraNotesEOMChange modulation depth for 14.75MHz EOM

I increased the power to the 14.75MHz EOM from 0.5 dBm to 3.5 dBm. This was done by changing the attenuator from -6dBm to -3dBm.

As a quick test to see improvement in electronic noise level, I increased the detection gain. The modulation depth was changed from 0.14 to 0.2 rad (following the EOM's paramters in psl:855). I could not see any improvement yet. So I'll try to damp the mechanical peaks in the signal so that flat noise level can be measured better.

 

The slope of error signal for RCAV and ACAV are 44.25/57.62 kHz/V

  913   Fri Apr 13 13:35:37 2012 Tara, FrankSummaryNoiseBudgetPDH readout noise level verification

we re-checked the electronic noise level for each PDH loop and also checked how the noise level rises with a shot noise limited light source (halogen bulb) using the exact same setup as we use daily.
Before we had only checked the individual parts, e.g. the shot noise limit of our RF-PD, not including the rest of our setup (mixer, LO or filter stages). This was just to confirm that nothing is broken and our PDs are still OK.

Measurements were taken right after the mixer / LP-filter, but still connected to PDH servo. This is OUT1 of the common path of the TTFSS-box  and the input on the front of our ACAV PDH servo. We blocked the laser and adjusted the power of the bulb and measured the electronic noise floor using the SR785. The dark noise spectrum is the one already shown in the last noise budget. Below the plots of noise level, measured around 500Hz (100 avgs, wide marker) vs different photocurrents of the PDs. DC impedance is 2kOhms, regular DC level for RCAV is 1.7V and 1.47V for ACAV. RF-impedance is the same as measured some time ago for those diodes. Data in folder 4/11/2012 on svn.

SN_RCAV.png  SN_ACAV.png

Conclusion: New measurements agree very well with the old measurements. So our PDs still work fine and there is no excess noise in our readout we missed.

  912   Fri Apr 13 03:15:12 2012 koji,frank,taraDailyProgressopticvibration damping on optics

We tried to damp mechanical peaks from each optics. For now, by putting a rubber piece on a mirror mount can suppress mechanical peaks effectively. We are still thinking about more robust way to damp the peaks.

    Beat signal has a lot of acoustic peaks from 100Hz up to 1kHz, and they may mask any improvement we work on flat noise. Damping them is necessary before we can work on the flat noise hidden underneath.

    By tapping each optic, we can see peaks raising up in beat signal or feedback signal to ACAV AOM. We used the feedback to ACAV AOM to identify peaks in ACAV path first. The curve mirror behind AOM has a strong peak which can be damped by a rubber cone placed on top of the mount, see fig1 below.

IMG_0731.jpg

fig1:  Mirror mount1, with a damping rubber on top.

     We also tried using different mounts to see if the peak would be reduced. The original mount was an anodized aluminium mount. We switched to different two stainless steel mounts, mount1 and mount2. The spectrum of the feedback signal to AOM (not calibrated) between two mounts with and without damping rubber are shown below. From the spectrum, there are not much different between the current anodized Al mount (not shown) and the steel mount in fig1.

damped.png

 

Note: We also tried to damp the mirror mount with small rubber pieces placed between the frame and the body of the mount, but it did not help at all. The springs of the mount are stronger than the rubber, so this method is not effective.

    To sum up,

  • we need to damp most of our optics. The current plan is to use a rubber cone and just place on top of the mirror mounts. We are also thinking about better damping schemes. 
  • There are not much different between a stainless steel mount [add model#], and an aluminium mount[add model#]. It is probably unnecessary to change mirror mounts.
  • We will order more of the rubber cones for damping.
  911   Thu Apr 12 22:22:12 2012 frank, taraDailyProgressNoiseBudgetElectronic noise + shot noise verification

We measured shot noise level with white light source. The noise level is slightly off from shot noise calculation in the noise budget.

  After identifying electronic noise in the detection part, we characterized shot noise in RCAV and ACAV systems.  We shined a white light source on the RFPD, and adjusted its power so that V_DC level was the same when the cavity was locked.  Then measured the noise at mixer out (out1 for RCAV system). This voltage noise has contribution from shot noise and electronic noise. It can be converted to frequency noise by multiplying with the slope of error signal.

  ACAV RCAV
Vdc [V] 0.4 0.1
Vnoise(flat) [nV/rtHz] 49.4 40.7
Slope [kHz/V] 81.7 40.3
 f Noise [mHz/rtHz]  4.0

 1.64

 

  The frequency noise calculated in the last row has contribution from shot noise and electronic noise (from previous entry). By subtracting(quadraturely) the electronic noise, we should obtain the contribution from shot noise only. Electronic noise (from previous entry) are 1.8 and 1 mHz/rtHz for ACAV and RCAV, respectively. This gives shot noise level = 3.6/1.3 mHz/rtHz for ACAV/RCAV. The calculation in the noise budget gives  1.6/0.9 mHz/rtHz.  The measured and calculated results do not match. I think because the error in modulation index, finesse, cavity mode matching are too large. The results are summarized in the table below. I will use the measured shot noise/ electronic noise in the noise budget for now.

  ACAV RCAV
Electronic noise(measured)[mHz/rtHz] 1.8 1
Shot+electronic noise [mHz/rtHz] 4 1.64
Shot noise [mHz/rtHz] 3.6 1.3
Calculated shot noise* [mHz/rtHz] 1.6 0.9

 

* The calculated shot noise use 1mW power into each cavity. Modulation index = 0.14. The following numbers are in [ACAV/RCAV] format.  Finesse = (7500/9700), Visibility = (90%/80%)

  910   Thu Apr 12 13:58:17 2012 FrankDailyProgressNoiseBudgetlow frequency noise source

HEPA.png

Quote:

i have identified part of the low frequency noise source from yesterdays measurement - air fluctuations. We still had the HEPA fans on maximum.

 

  909   Wed Apr 11 20:30:50 2012 frank, taraDailyProgressNoiseBudgetElectronic noise verification

  We are checking the noise contribution from electronics readout of our system to get better noise budget estimation. We added detection noise from RCAV and ACAV systems in the noise budget. They are comparable to the estimated shot noise level.

    We measured the noise level of the PDH detection for RCAV and ACAV system, the corresponding error signal slope.The results are summarized in the table below.

Setup: 1mW input to each cavity, TTFSS: Common/Fast = 900/800,

  RCAV ACAV
Pwr input [mW] 1 1
V_DC (RFL RFPD) [V] 1.7 1.47
Err signal Slope [kHz/V] 40.3 81.7
Detection Noise [nV/rtHz] 35 23

 

Detection Noise x Err signal slope gives us the electronic noise contribution in absolute frequency unit. From the above table, we obtain

1 mHz/rtHz and 1.8 mHz/rtHz from RCAV and ACAV systems, respectively.

 The electronic noise from RCAV and ACAV systems are added to the noise budget. In the plot below, I removed the traces for Spacer noise and thermo optic noise to make the plot less crowded, but their contribution are included in the total noise.

beat_2012_04_11.png

 

More to come:

  • Shot noise measurement for ACAV/RCAV/beat
  • TTFSS OLG TF, suppressed laser frequency noise

 

  908   Wed Apr 11 14:31:52 2012 FrankDailyProgressNoiseBudgetlow frequency noise source

i have identified part of the low frequency noise source from yesterdays measurement - air fluctuations. We still had the HEPA fans on maximum.

  907   Wed Apr 11 14:22:47 2012 FrankNotesLaserlaser shutdown

pulling the switch for one of the HEPA fans triggered the laser and put it in standby mode - turned laser back on

  906   Wed Apr 11 02:44:29 2012 frank, taraDailyProgressopticbad PBS

Update, beat measurement after several optics replacement. Peaks around 10 Hz, 35 Hz show up this time.

    Optics that we replaced are:

  •  Beam splitter that divides the beam to ACAV and RCAV path. Now the new BS is 1" cube for large beam
  • Fixed the orientation of mirrors on the periscope and the turning mirror for ACAV RFPD. A few of them were flipped back causing stray light in the beam path.
  • Two of the mirrors on periscope had transmission of 2% or so, we replaced with a high reflective ones (0.1% transmission).

The problem with the curve mirror from last entry has not been fixed yet. It turns out that the mirror we borrow from 40m is worse than the one we have (surface is more milky), so we leave the original mirror as it is.

Note: The beat measurement was done when the air springs were inactive. Noise at high frequency goes down a bit.

The power input to each cavity is 1mW, setup on PLL is 1kHz input range, with gain = 200.

beat_2012_04_10.png

  905   Tue Apr 10 00:50:56 2012 frank, taraDailyProgressopticbad PBS

We noticed wide angle scattered light behind the PBS in front of RCAV. The scattering source is probably the curved mirror behind RCAV AOM. We borrowed the similar mirror from 40m and will try to compare them.

      The wide angle scattered light behind the PBS in front of RCAV might contribute to the noise in beat signal. The picture shows the scattered light with area larger than the half inch PBS cube. This picture was taken when the beam's polarization was changed to P-polarization so that most of the light was reflected from the PBS. With small transmitted light through the PBS, the scattered light can be seen clearly behind the PBS, see here

     After the inspection, it is very likely that the curve mirror behind RCAV AOM is the source. So we borrowed another R=0.3 mirror from 40m to see if it will be better or not, this will be done soon.

     Note: during the inpsection, we also identified another bad PBS,pic. This is the one in front of RCAV AOM. Its center surface looks dirty, so we replaced it with a better one.

  904   Mon Apr 9 23:05:44 2012 taraDailyProgressSeismicSeismic coupling from curtain frame to beat

Ting's code for new coating thermal noise is attached. This is the code used for the calculation in their paper (not published yet). They use loss in shear and bulk mode which are assumed to be equal to the loss measured from ring down. The result is ~5% different from the calculation from Harry et al's result.

    We talked to Huan about how their coating Brownian noise calculation differs from that of Harry etal. The main points are:

  • different notation for loss angles
  • light penetration in the coating is considered
  • correlation between substrate surface and coating noise

Since phi_bulk and phi_shear are not well studied in the literature, the exact values are undetermined. By setting them to be equal to the regular phi obtained from ring down measurement, the result of the coating noise is not significantly different from the model we have been using.

  903   Sun Apr 8 23:35:05 2012 taraDailyProgressSeismicSeismic coupling from curtain frame to beat

  I used ciplot command to plot the noise budget with confidence region. 

beat_ciplot.png

Quote:

http://lmgtfy.com/?q=matlab+ciplot

 

  902   Fri Apr 6 01:36:39 2012 Tara, FrankSummaryNoiseBudgetACAV loop changes

summary of all changes made and more detailed plots will be posted soon, so check back later

writing in progress

  • replaced New Focus power supply for RFPD with Agilent power supply (+/-15V)
  • added isolation transformer between mixer LO and main splitter of 14.75MHz LO
  • changed gain of input stage from PDH-box from 10 to 20
  • replaced thickfilm resistors in input stage with thin film ones
  • added offset potentiometer to input opamp
  • added 25MHz HP-filter to AOM driver/amplfier

ACAV loop is now completely free from line harmonics and the in-loop level dropped to ~10nV/rtHz (includes 7nV/rtHz from analyzer). Mixer dark noise is ~25nV/rtHz.

  901   Fri Apr 6 01:07:47 2012 taraDailyProgressNoiseBudgetThermoelastic noise from substrate

I corrected the code for substrate thermoelastic noise (TE) in my noise budget. The substrate thermoelastic of 8 inch cavity will not be a problem, but it will be comparable to coating thermal noise around 10 Hz for 1.45" cavity.

 

     After reviewing the papers about measurement of thermoelastic noise in substrate, I realized that I have not fixed my calculation for substrate TE as noted in both publications by Numata et al (2003) and Black et al (2004). Apparently, the calculation from Cerdonio et al(2003) uses different notion of beam radius, and misses one factor of pi.  The new result is plotted below. It is about a factor of 1.5 higher than the old one at adiabatic limit (high f), but it is still smaller than the estimated coating thermal noise, see figure 1.

 corrected.png

fig1: TE noise is corrected and plotted in comparison with the previous result.

     However, for a planned 1.45" long cavity, due to the smaller spot size on the mirror, TE noise is very close to the coating thermal noise around 3 Hz up to50 Hz, see figure 2 below. So this will be another issue to keep in mind.  Note: shot noise seems to be very high, I'll double check the result again if it is correct or not. I just changed the cavity length parameter and ran the code to get the result.

beat_145in.png

fig2: Noise budget for 1.45" long cavity.

  900   Fri Apr 6 01:03:01 2012 frank, taraDailyProgressBEATground loop problem

We fixed the ground loop problem in ACAV setup and got rid of most of the harmonic lines in beat signal.

    The ground loop problem in our current setup comes from the common ground of the two Marconis. The first one is for 14.75 MHz EOM. Its signal is split, and sent to demodulate the signal from ACAV RFPD. The second Marconi is for driving the AOM around 80 MHz for frequency lock. By using a transformer between the mixer (for PDH demodulation) and the LO signal from the first Marconi, we broke the ground loop, hence got rid of the harmonic lines in the signal.

beat_2012_04_05.png

  899   Fri Apr 6 00:34:28 2012 ranaHowToNoiseBudgetscattered light hunting

How to find parasitic scatterers by the GEO600 gang.

  898   Wed Apr 4 23:58:43 2012 taraNotesNoiseBudgetthermal noise from spacer + support

Following the calculation from Kessler, I estimated brownian noise from the spacer and the o ring support from our setup. From the cursory check, it seems that we don't have to worry about both sources too much.

      Kessler et al. refined the calculation for brownian noise of a spacer from Numata's et al and included  Brownian noise of viton supports. For spacer's noise, they corrected the result for a cavity with a hole along the cavity's axis, and also did the FEA simulation with COMSOL for the mirrors that are smaller than the diameter of the spacer. For their chosen geomtry, the noise from the spacer, as obtained from FEA, can be 30% larger than the analytical result.

    So, as a quick check for our cavity, I used their analytical result and increased the result by 30% to get an estimate. The new spacer noise is about an order of magnitude below the coating noise, so it should not be a problem.

    For viton noise calculation, they assumed a 4-point supported cavity, and calculated the energy stored in shear deformation, then used fluctuation-dissipation theorem(FDT) to compute the displacement fluctuation. However, our cavity is supported by two o-rings wrapping around the cavity's groove and sitting on two  U-shape teflon pieces. I don't know the exact thickness of our o-rings, so I use (1/8)" = r_o . Assuming that the surface area is  pi* cavity's radius * r_o *sqrt(2), and thickness of the o ring under pressure = 1.5 r_o. [add pic], I can get the noise contribution from the support. Parameters for O-rings' are assumed to be the same as those of viton in the paper. The result is about the same as substrate's Brownian noise, which is not very threatening for our experiment. I believe that the actual number will be even lower, since my estimation exaggerates, to get the upper bound, the surface area of the o ring to be half of the spacer's perimeter times the ring's thickness. The actual shear deformation should be localized in smaller area.

 Parameters for our cavities can be found here.

  

 

beat_nb.png

  897   Wed Apr 4 18:57:11 2012 ranaDailyProgressSeismicSeismic coupling from curtain frame to beat

http://lmgtfy.com/?q=matlab+ciplot

  896   Tue Apr 3 20:56:10 2012 frank, taraDailyProgressSeismicSeismic coupling from curtain frame to beat

We measured the beat signal after we fixed the wiring problem. We are close to what we had before, but we still have a scattering light problem.

      Just after we fixed the cable wiring between the table and the frame on 3/30, we measured the beat signal (beat 03/30, blue). There was a hughe scattering noise bump from 100-200 Hz, and it was not stable. We did not see this before (beat 03/12, pink).  We found that there were plenty of dust on the periscope mirrors, lenses in front of RFPD. These optics are in the sensing path, and are more sensitive to scattering light. After cleaning them, the beat signal is better now (beat 04/03). The bump at low frequency is still higher than before, but now it is stable. 

Note that the acoustic peaks around 1kHz are not reduced from fixing the cable, but the bump at low frequency is slightly lower. This is reasonable, the cables should be very soft at high frequency, and do not transfer any vibration from the frame to the table at acoustic bandwidth.

beat_2012_04_03.png

     Other changes we did:

  • replaced the PBS before ACAV AOM with a new one. The old one has defect coating, which we can see by eys, and causes extra back reflection.
  • replaced the PBS in front of RCAV. This one also has high back reflection.
  • re-adjusted the AOM angle. It was tilted down a bit, and this causes extra beam distortion. The beam ellipticity changes from ~0.7 to 0.88 when the AOM is almost parallel to the table surface.
  • replaced translational stage for the curve mirror behind ACAV AOM. Now it should be more stable ( but I don't see any obvious suppression in acoustic peaks yet).
  • sealed the gap between the curtain frame and the plastic covers on top of the table where dust might fall off.
  • change the air spring setup ( I'm not sure about the details, need to ask Frank)

      It is very likely that the when we removed all the cables on the table, dust was stirred up and stuck on the optics, because they are dirtier than usual. We might need to clean more optics on the table. However, from today measurement, it seems that the bump at low frequency might be the effect from the seismic as well (from the feature of the peaks @35 and 55 Hz). Noise budget from seismic will be revisited, also the flat noise at high frequency will be investigated next.

ELOG V3.1.3-